Aluminium compounds (herein also referred to as “aluminium”), including aluminium phosphate (AlPO4), aluminium hydroxide (Al(OH)3), and other aluminium precipitated vaccines are currently the most commonly used adjuvants with human and veterinary vaccines. The adjuvants are often referred to as “alum” in the literature.
Aluminium adjuvants have been used in practical vaccination for more than half a century. They induce early, high-titre, long-lasting protective immunity. Billions of doses of aluminium-adjuvated vaccines have been administered over the years. Their safety and efficacy have made them the most popular adjuvants in vaccines to date. In general, aluminium adjuvants are regarded as safe when used in accordance with current vaccination schedules.
In human vaccinations, of old, aluminium adjuvants have been used in tetanus, diphtheria, pertussis and poliomyelitis vaccines as part of standard child vaccination programmes. Aluminium adjuvants have also been introduced into hepatitis A and hepatitis B virus vaccines and Japanese encephalitis virus (also referred herein as “JEV”) vaccines. Other aluminium-adsorbed vaccines against, for example, anthrax, are available for special risk groups. In veterinary medicine aluminium adjuvants have been used in a large number of vaccine formulations against viral and bacterial diseases, and in attempts to make antiparasite vaccines.
Adjuvants typically serve to bring the antigen, the substance that stimulates the specific protective immune response, into contact with the immune system and influence the type of immunity produced, as well as the quality of the immune response (magnitude or duration); Adjuvants can also decrease the toxicity of certain antigens; and provide solubility to some vaccines components. Studies have shown that many aluminium-containing vaccines cause higher and more prolonged antibody responses than comparable vaccines without the adjuvant. The benefit of adjuvants has usually been observed during the initial immunization series rather than with booster doses.
There are three general types of aluminium-containing adjuvants:
Aluminium hydroxide, Aluminium phosphate and Potassium aluminium sulphate (collectively often referred to as “Alum”).
The effectiveness of each salt as an adjuvant depends on the characteristics of the specific vaccine and how the manufacturer prepares the vaccine. To work as an adjuvant, the antigen is typically adsorbed to the aluminium; that is, it is clumped with the aluminium salt to keep the antigen at the site of injection.
Not all vaccines contain aluminium salts. Sometimes an adjuvant may not have been needed or another adjuvant was selected. Examples of commercial vaccines that do not contain aluminium salts are inactivated Polio Virus (IPV) vaccine, measles, mumps and rubella vaccine (MMR), varicella vaccine, Meningococcal conjugate (MCV4) vaccine, and influenza vaccines. That the commercial vaccines do not contain aluminium salts does typically not mean that an aluminium salt would not work. It just means that for some reason another adjuvant was selected.
Examples of US licensed vaccines for children that contain aluminium adjuvants are: DTP (diphtheria-tetanus-pertussis vaccine); DTaP (diphtheria-tetanus-acellular pertussis vaccine); some but not all Hib (Haemophilus influenzae type b) conjugate vaccines; Pneumococcal conjugate vaccine; Hepatitis B vaccines; Hepatitis A vaccines; Human Papillomavirus vaccine; Anthrax vaccine; and Rabies vaccine.
Aluminium is a very abundant element in our environment. It is in many foods we eat, many personal hygiene products we apply to our skin (deodorants, for example), and many medicines we ingest. Various government agencies establish guidelines for exposure to potentially toxic substances. These guidelines are called “minimal risk levels”—the maximum amount that one can be exposed to over time-usually on a daily basis-without expected harm.
The US Agency for Toxic Substances and Disease Registry (ATSDR) estimated these levels for infants taking into account the amount of aluminium (e.g. in form of a salt) a child would eat as well as receive by injection of vaccines. The body burden of aluminium from both sources is below the minimal risk level except transiently following vaccinations; since 50-70% of injected aluminium is excreted within 24 hours, this is believed to have no negative effect.
Aluminium hydroxide and aluminium phosphate adjuvants are generally prepared by exposing aqueous solutions of aluminium ions, to usually slightly alkaline conditions in a well-defined and controlled chemical environment. Various soluble aluminium salts can be used for the production of aluminium hydroxide. Anions present at the time of precipitation may coprecipitate (for review see, Lindblad, E B (2004) Immunol. and Cell Biol. Vol 82: 497-505).
Aluminium salt is also used in the manufacture and composition of medicaments. For instance, factor VIII is purified from plasma cryoprecipitate. The precipitate is solubilised, absorbed on aluminium hydroxide and then treated to inactivate lipid enveloped viruses. After several other processing steps the concentrate is used to treat hemophilia A patients (Burnouf T, (1991) Vox Sang. Vol 60: pp 8-15).